Endometriosis is a chronic gynaecological condition causing a whole host of debilitating symptoms, including "killer cramps", long periods, nausea, vomiting, and even infertility.
Now, a new study has put our extraordinary ignorance front and centre. It suggests that the medical community has been underestimating one of the most intense and frequent symptoms of endometriosis: persistent fatigue.
"Although chronic fatigue is known to be one of the most debilitating symptoms of endometriosis, it is not widely discussed and few large studies have investigated it," said lead author Brigitte Leeners, an expert in obstetrics and gynaecology at the University Hospital Zurich.
Leeners set out to investigate. Her team provided a questionnaire to 1120 women, half of whom had endometriosis and half of whom did not.
The findings suggest that women diagnosed with endometriosis are more than twice as likely to report symptoms of fatigue than unaffected women.
Even more convincing, the results remained significant even when the researchers took into account other factors that might be contributing to the fatigue, like pain, insomnia, stress, depression, BMI and motherhood.
"These findings suggest that endometriosis has an effect on fatigue that is independent of other factors and that cannot be attributed to symptoms of the disease," said Leeners.
Scientists think that endometriosis is caused when the endometrium - the cells lining the uterus - migrate outside of the womb, where they start to cause all sorts of problems.
As such, Leeners and her team have theorised that these endometrial lesions may be activating the immune system by causing inflammation. Their theory rests on past research, which suggests that cytokines, a type of protein associated with an activated immune system, can play a role in fatigue.
But the researchers didn't just ask participants about fatigue, they also asked them about their medical and family history, their life style and mental state, and whether, on the flip side, they had experienced any insomnia.
When analysing all of this data, the researchers found that women with fatigue and endometriosis experienced a seven-fold increase in insomnia, a four-fold increase in depression, a two-fold increase in pain and a nearly 1.5-fold increase in occupational stress.
In a vicious cycle, the study concludes that chronic exposure to high stress "can result in adrenal fatigue which could be another possible explanation for a relation between endometriosis and fatigue."
Along with the rude awakening, comes a few suggestions for how doctors can improve the way they treat patients with endometriosis.
"In addition to treating endometriosis, it would be beneficial to reduce insomnia, depression, pain and occupational stress in order to better manage fatigue," the study suggests.
The research also puts a focus on coping mechanisms for patients - an important step for a disease that has no cure.
The team noted that some of the participants who had found positive ways to cope with their endometriosis reported suffering from less depression, while negative coping strategies made the fatigue far worse.
The researchers, therefore, suggest that "fatigue in endometriosis could be a result of poor disease coping."
In other words, living with endometriosis is awful, but when patients are not given proper support from their health practitioners, it makes it all so much worse.
"We believe that in order to improve the quality of life for women with this condition, investigating and addressing fatigue should become a routine part of medical care, and doctors should investigate and address this problem when they are discussing with their patients the best ways to manage and treat the disease," said Leeners.
"It would also help these women if steps were taken to reduce insomnia, pain, depression and occupational stress."
That's the very least we can do.
The study has been published in Human Reproduction.